1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor. The present invention also relates to an image forming method, an image forming apparatus and a process cartridge using the electrophotographic photoreceptor, such as copiers, facsimile machines and laser printers.
2. Discussion of the Background
Recently, development of information processing systems utilizing electrophotography has been remarkable. In particular, optical printers in which information converted to digital signals is recorded using light have been dramatically improved in print qualities and reliability. This digital recording technique is being applied not only to printers but also to copiers which can produce documents including color images. Thus, photoreceptors are required to produce high quality images and to have high durability.
To produce high definition images, the particle diameter of toner, both pulverized toner and polymerization toner, is decreased more and more. However, such a toner having a small particle diameter has a low fluidity and a relatively large adherence. Therefore the toner has poor cleanability. As the diameter of toner decreases, the surface area of the toner per unit volume increases. In attempting to improve fluidity, a large amount of external additive is added to a toner having a small particle diameter. However, good cleanability cannot be imparted to toner by such a technique.
On the other hand, in attempting to produce a high definition image, a spherical toner which has good development and transfer properties is commonly used. The spherical toner has a high fluidity but tends to rotate on the surface of the photoreceptor. Therefore the spherical toner slips through a cleaning blade, and thereby the toner is insufficiently cleaned, especially in a high-speed image forming apparatus.
In addition, there are many types of cleaning methods such as brush cleaning methods and blade cleaning methods etc. Among these cleaning methods, the blade cleaning methods are typically used because of having a simple structure and lower cost.
The cleanability of a spherical toner having a small particle diameter can be improved by improving the toner or the cleaning process. For example, as one technique for improving toner, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2003-131537 discloses an image forming apparatus. The image forming apparatus uses a toner having a diameter (d) of from 4 to 10 μm, and a flattening factor t/d, a ratio of a diameter (d) and a thickness (t) of the toner particle, of from 2 to 5. By using such a toner, the stress applied to the toner by a cleaning blade can be decreased, and the toner collected by the cleaning device is recycled. This image forming apparatus includes the cleaning blade made of a rubber, and a means of feeding toner collected from the cleaning device to a developing device.
As one technique for improving the process, JP-A 2002-221886 discloses an image forming method using a photoreceptor having a surface layer including a siloxane-containing resin. In the method, the following relationship is satisfied;0.2≧Y100−Y0≧0.01, 2.95≧Y100/Y0≧1.15wherein Y0 (N·m) represents an average value of dynamic torque generated between the photoreceptor and the cleaning blade, and Y100 (N·m) represents an average value of dynamic torque generated between the photoreceptor and the cleaning blade when a 100% solid image is formed on the photoreceptor.
However, these methods cannot sufficiently improve the cleanability of a spherical toner having a small particle diameter.